Received cashiers check from money market account, was beneficiary, mothers death not filed with state yet. Do I claim anywhere on my tax return? Or report as income? Under 50,0000

In the US? Unless your state has an inheritance tax for $50,000 or less, you own nothing. Where do you live? If no taxes from the state, you are well under Federal tax requirements. Congratulations!

Yuo do not report it as income. There are no federal taxes on inheritance, so nothing to report to the feds. There are a few states that have inheritance taxes, and most exempt inheriatnce from a parent, so as ma0641 said we need to now what state you and your mother lived in.